U.S. patent number 6,166,089 [Application Number 09/428,848] was granted by the patent office on 2000-12-26 for prodrugs with enhanced penetration into cells.
This patent grant is currently assigned to D-Pharm, Ltd.. Invention is credited to Alexander Kozak.
United States Patent |
6,166,089 |
Kozak |
December 26, 2000 |
**Please see images for:
( Certificate of Correction ) ** |
Prodrugs with enhanced penetration into cells
Abstract
The invention relates to a pharmaceutically acceptable prodrug
which is a covalent conjugate of a pharmacologically active
compound and an intracellular transporting adjuvant, characterized
by the presence of a covalent bond which is scission-sensitive to
intracellular enzyme activity. The prodrug may be used in a
technique for treating a condition or disease in a mammal related
to supranormal intracellular enzyme activity, whereby on
administering it to a human having such condition or disease, the
bond is broken in response to such activity, and the
pharmacologically active compound is activated selectively within
cells having such supranormal intracellular enzyme activity.
Inventors: |
Kozak; Alexander (Rehovat,
IL) |
Assignee: |
D-Pharm, Ltd. (Rehovot,
IL)
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Family
ID: |
23906125 |
Appl.
No.: |
09/428,848 |
Filed: |
October 28, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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479959 |
Jun 7, 1995 |
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481243 |
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Current U.S.
Class: |
514/642; 514/144;
514/557 |
Current CPC
Class: |
A61K
31/352 (20130101); C07F 9/10 (20130101); A61K
47/544 (20170801); A61K 47/542 (20170801); Y10S
514/826 (20130101) |
Current International
Class: |
A61K
31/352 (20060101); A01N 033/12 () |
Field of
Search: |
;514/144,557,642 |
References Cited
[Referenced By]
U.S. Patent Documents
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4654370 |
March 1987 |
Marriott, III et al. |
5149794 |
September 1992 |
Yatvin et al. |
5227514 |
July 1993 |
Meul et al. |
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Foreign Patent Documents
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0275005 |
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Jul 1988 |
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EP |
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0325160 |
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Jul 1989 |
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EP |
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3133987 |
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Jun 1991 |
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JP |
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679856 |
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Apr 1992 |
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CH |
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8905358 |
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Jun 1989 |
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WO |
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9000555 |
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Jan 1990 |
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WO |
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9010448 |
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Sep 1990 |
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WO |
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9116920 |
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Nov 1991 |
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WO |
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9300910 |
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Jan 1993 |
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WO |
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9408573 |
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Apr 1994 |
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WO |
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Other References
Hadad, S., et al., Pharmacokinetic Analysis and Anticonvulsant
Activity of Two Polysteric Prodrugs of Valproic Acid,
Biopharmaceutics & Drug Disposition, vol. 14, pp. 51-59 (1993).
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Mergen, F., et al., Antiepileptic activity of
1,3-dihexadecanoylamino-2valproyl-propan-2-ol, a Prodrug of
Valproic Acid Endowed with a Tropism for the Central Nervous
System, J. Pharm.Pharmacol., vol. 43, pp. 815-816 (1991). .
NITS Technical Notes. No. 9, 1984, "Prodrugs based on
phpospholipid-nucleoside conjugates" Springfield, VA, p. 630. .
Stuttgart, DE, Geb. 1992; European J. of Pharmaceutics and
Biopharmaceutics, 38(1):1-6. O. Vaizoglu et al., Jul. 26, 1989,
EP-A-0325 160 (Hoechst A.G.). .
Hostetler et al., Jun. 1991, "Phosphatidylaazothymidine. Mechanism
of antiretroviral action in cem cells." J. Biol. Chem.
266(18):11714-11715. .
Gusovsky et al., Feb. 1990, "Mechanism of maitotoxin-stimulated
phosphoinositide breakdown in HL-60 cells." J. Pharmacol. Ex. Ther.
252(2):469-470. .
Govez-Cambronero et al., Apr. 1991, "Platelet-activating induces
tyrosine phossssphorylation in human neutrophils." J. Biol. Chem.
266(10):6240-5. .
Natarajan et al. "Activation of endothelial cell phospholipase D by
hydrogen peroxide and fatty acid hydroperoxide." J. Biol. Chem
268(2):930-7. .
Coorsen et al., "GTP.gamma.S and phorbol ester act synergistically
to stimulate both calcium independent secretion and phospholipase D
activity in permeabilized human platerits. Inhibition by BAPTA and
analogs" FEBS Lett. 316(2):170-4. .
Duan et al., Feb. 1994, "Conversion to CA(2+)-independent form of
Ca2+/calmodulin protein kinase II in rat pancreatic acini."
Biochem. Biophys. Res. Commun. 199(1):368-373..
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Primary Examiner: Carr; Deborah D.
Attorney, Agent or Firm: Davidson, Davidson & Kappel
LLC
Parent Case Text
This application is a continuation of U.S. patent application Ser.
No. 08/479,959, filed Jun. 7, 1995, which is a continuation-in-part
of U.S. application Ser. No. 08/481,243, filed on Aug. 21, 1995 as
a U.S. nationation stage application of PCT/GB94/00669, the
disclosures of which are incorporated by reference herein in their
entirety.
Claims
What is claimed is:
1. A method for treating epilepsy in a mammal comprising
administering to a mammal in need of treatment, an effective amount
of a pharmaceutically acceptable prodrug comprising valproic acid
or a pharmaceutically acceptable derivative thereof covalently
bonded to a quaternary derivative of
lysophosphatidyl-ethanolamine.
2. The method according to claim 1, wherein said quaternary
derivative of lysophosphatidyl-ethanolamine is
1-heptanoyl-sn-glycero-3-phosphorylcholine.
3. The method according to claim 1, wherein said quaternary
derivative of lysophosphatidyl-ethanolamine is
1-hexadecanoyl-sn-glycero-3-phosphorylcholine.
4. A method for treating epilepsy in a mammal comprising
administering to a mammal in need of treatment, an effective amount
of a pharmaceutically acceptable prodrug comprising valproic acid
or a pharmaceutically acceptable derivative thereof covalently
bonded to a quaternary derivative of
lysophosphatidyl-ethanolamine,
wherein said covalent bond is scission-sensitive to supranormal
intracellular enzyme activity;
said prodrug being cell membrane permeable and said covalent bond
being cleaved in the presence of said supranormal intracellular
enzyme activity and wherein cleavage of said covalent bond results
in selective intracellular accumulation of therapeutic amounts of
valproic acid within cells having said supranormal intracellular
enzyme activity.
5. The method according to claim 4, wherein said quaternary
derivative of lysophosphatidyl-ethanolamine is
1-heptanoyl-sn-glycero-3-phosphorylcholine.
6. The method according to claim 4, wherein said quaternary
derivative of lysophosphatidyl-ethanolamine is
1-hexadecanoyl-sn-glycero-3-phosphorylcholine.
7. The method according to claim 4, wherein said intracellular
enzyme activity is related to an epileptic disease.
8. The method according to claim 7, wherein said intracellular
enzyme is lipase.
9. The method according to claim 8, wherein said lipase is
phospholipase.
10. The method according to claim 9, wherein said phospholipase is
phospholipase A.sub.2.
11. A pharmaceutically acceptable prodrug comprising vaproic acid
or a pharmaceutically acceptable derivative thereof which is
covalently bonded to an intracellular transporting adjuvant,
wherein said intracellular transporting adjuvant is quatenary
derivative of lysophosphatidyl-ethanolamine.
12. The prodrug according to claim 11 wherein said quaternary
derivative of lysophosphatidyl-ethanolamine is
1-heptanoyl-sn-glycero-3-phosphorylcholine.
13. A pharmaceutically acceptable prodrug comprising valproic acid
or a pharmaceutically acceptable derivative thereof which is
covalently bonded to an intracellular transporting adjuvant, said
intracellular transporting adjuvant comprising a compound selected
from the group consisting of C.sub.3-20 fatty acid monoglycerides,
C.sub.3-20 fatty acid diglycerides, hydroxy-C.sub.2-6 -alkyl esters
of lysophosphatidic acids, lyso-plasmalogens, lysophospho-lipids,
lysophosphatidic acid amides, glycerophosphoric acids,
lyso-phosphatidalethanolamine, lysophosphatidyl-ethanolamine,
N-mono-(C.sub.1-4)-alkyl and N,N-di-(C.sub.1-4)-alkyl and
quaternary derivatives of the amines thereof, wherein said covalent
bond is scission-sensitive to intracellular enzyme activity related
to an epileptic disease, and wherein said intracellular
transporting adjuvant is 1
-heptanoyl-sn-glycero-3-phosphorylcholine.
14. The prodrug according to claim 1 wherein said quaternary
derivative of lysophosphatidyl-ethanolamine is
1-hexadecanoyl-sn-glycero-3-phosphorylcholine.
Description
FIELD OF THE INVENTION
The present invention relates to a technique for treating a
condition or disease in a mammal, including humans, related to
supranormal intracellular enzyme activity, and to a prodrug useful
in treating such a condition or disease.
BACKGROUND OF THE INVENTION
Many of the most prevalent diseases in humans including ischemia,
stroke, epilepsy, asthma and allergy are all believed to be related
to the phenomenon of cell hyperexcitation, a term used herein to
denote supranormal intracellular enzyme activity. Certain
pharmacological strategies are therefore aimed at inhibiting this
detrimental degradative activity.
In contrast to such known strategies which are aimed at suppressing
this degradative activity, it would be advantageous to be able to
selectively target diseased cells characterized by enzyme
hyperactivity, so as to introduce a pharmacologically active
molecule in the form of a prodrug into the cell, whereby such
hyperactivity would act on the prodrug, so that the
pharmacologically active molecule accumulates in the diseased cells
rather than in the healthy cells.
Different types of intracellular enzyme systems are known to be
significantly elevated in pathological conditions, and may be used
to achieve preferential release of the active drug compound within
the diseased cells. Candidate enzymes that could be utilized to
activate the prodrugs according to the present invention include
lipases, proteases or glycosidases. By way of example, in many
diseases cell membranes are broken down due to abnormal
intracellular lipase activity.
The use of prodrugs to impart desired characteristics such as
increased bioavailability or increased site-specificity on known
drugs is a recognized concept in the state of the art of
pharmaceutical development. The use of various lipids in the
preparation of particular types of prodrugs is also known in the
background art. In none of those instances are the prodrugs
characterized in that they achieve preferential accumulation of the
drug within the diseased cells of the organ, by activation with
intracellular lipases. Rather, they provide for the drug to be
transported to a specific site, or to be released within a specific
organ.
This approach is exemplified in the case of the phospholipid
prodrugs of salicylates and non-steroidal anti-inflammatory drugs
disclosed in WO 91/16920 which, taken orally, protect the gastric
mucosa and release the active principle in the gut.
In other examples of phospholipid prodrugs, formulation of the
prodrugs into liposomes or other micellar structures is the feature
that enables their preferential uptake, for instance by macrophages
or by liver cells as in the case of the phospholipid conjugates of
antiviral drugs disclosed in WO 90/00555 and WO 93/00910.
Generally, viral infection is not associated with supranormal
phospholipase activity and antiviral phospholipid conjugates do not
teach or suggest activation of the drug preferentially in the
diseased cells, or in the infected cells as in the case of the
phospholipid conjugates of antiviral nucleotides and anti-sense
oligonucleotides, such as those disclosed in WO 90/00555, in WO
90/10448 and in NTIS Technical Notes, no. 9, page 630, Springfield,
Va., US, 1984.
In other instances specific types of polar lipids are used to
target the prodrugs to intracellular organelles as in the case of
the antiviral and antineoplastic nucleosides disclosed in U.S. Pat.
No. 5,149,794. Additional types of lipids have also been used in
specific types of prodrugs such as EP A-325160 which discloses
glycerin esters of ACE inhibitors, which form micelles absorbed
from the intestine into the lymphatic system, thereby bypassing the
liver and having increased access to the central nervous system,
for use in the treatment of hypertension and cognitive dysfunction.
The ACE inhibitors undergo enzymatic cleavage and exert their
therapeutic effects extracellularly.
Other types of lipophilic carriers that facilitate intracellular
transport are known in the art, as in CH A-679856 which discloses
the use of salicyloyl-carnitine for the treatment of pain, and in
WO 89/05358 which discloses modified oligonucleotide antisense
drugs, transported into cells by attachment of apolar groups such
as phenyl or naphthyl groups.
Different classes of pharmacologically active molecules can be
administered as prodrugs according to the principles of the present
invention. Candidates include anti-inflammatory drugs,
anti-epileptic drugs, protease inhibitors, and anti-tumor drugs. A
non-limiting example of such pharmacologically active molecules is
a calcium chelating agent, which would have many advantages over
drugs presently used for the treatment of calcium associated
disorders.
Intracellular calcium is an important determinant for cell death,
irrespective of the initial insult sustained by the cell. It may be
involved in cell death in lymphocyte and killer cell mediated
damage of target cells, in organ damage during transplantation, and
in other types of tissue damage including ischemic insults. Calcium
channel blockers or cell membrane permeable forms of calcium
chelators have been suggested to protect against tissue injury or
to decrease tissue damage. Thus, it will be apparent that the
present invention has potential use (in the embodiment employing a
calcium chelator) in relation to these circumstances
The cell damage occurring in ischemia may be secondary to the
influx and/or intracellular release of Ca.sup.2+ ions (Choi, Trends
Neurosci., 1988, 11, 465-469; Siesjo and Smith,
Arzneimittelforschung, 1991, 41, 288-292). Similarly, calcium
influx appears to play an important role in the genesis of
epileptic seizures. Although a significant portion of intracellular
calcium arrives from intracellular stores, current research
suggests that calcium entry blockers may have anticonvulsant
activity (see e.g. Meyer, 1989, Brain Res. Rev. 14, 227-243).
Drugs which are currently or potentially useful for treatment of
calcium associated disorders include: (1) calcium channel blockers,
(2) drugs affecting calcium balance by modification of
intracellular calcium storage sites, and (3) intracellular calcium
chelating agents. Calcium channel blockers used in clinical
practice are represented by Verapamil, Nifedipine and Diltiazem.
The major toxicities associated with the use of such compounds
involve excessive vasodilation, negative inotropy, depression of
the sinus nodal rate, and atrial ventricular (A-V) nodal conduction
disturbances. Drugs affecting calcium mobilization and/or
sequestration, like calcium channel blockers, exhibit rather narrow
specificity.
Though the use of calcium chelators for reducing injury to
mammalian cells is disclosed in WO 94/08573, there are no
intracellular calcium chelating agents suitable for clinical
requirements. Existing cell membrane permeable calcium chelators
include acetoxymethyl esters such as EGTA-AM (ethylene-1,2-diol bis
2-aminoethyl ether N,N,N',N',tetra-acetic acid acetoxymethyl ester)
EDTA-AM (ethylene-1,2-diamine tetra-acetic acid acetoxymethyl
ester), and BAPTA-AM (1,2-bis 2-aminophenoxy
ethan-N,N,N',N'-tetra-acetic acid acetoxymethyl ester). These known
complex molecules, are digested by ubiquitous esterases, thus
causing activation of the chelator in the intracellular space in a
manner which is random and uncontrolled, being unrelated to cell
activity.
It will also be self-evident that a similar concept can be applied
to the treatment of conditions or diseases other than those related
to the intracellular level of Ca.sup.2+ ions. By way of example, if
the active entity incorporated in the prodrug molecule is a protein
kinase inhibitor, after administration of the prodrug the inhibitor
would be accumulated in a cell exhibiting abnormal proliferation,
thus providing potentially an important tool for use in antitumor
therapy.
SUMMARY OF THE INVENTION
In accordance with one object of the invention, there are provided
prodrugs which selectively undergo activation to release
pharmacologically active compounds in hyperactivated cells. In
accordance with another object of the invention, the
pharmacologically active compound is released from the prodrug in
response to enzyme activity in the targeted cells. In accordance
with yet another object of the invention, the pharmacologically
active compound, selectively accumulated in a cell characterized by
a relatively raised level of enzyme activity therein, is trapped in
the cell and therefore exhibits an enhanced desired activity
therein.
The present invention accordingly provides in one aspect, a prodrug
which is a covalent conjugate of a pharmacologically active
compound and an intracellular transporting adjuvant, characterized
by the presence of a covalent bond which is scission-sensitive to
intracellular enzyme activity.
In another aspect, the present invention provides a technique for
treating a condition or disease in a mammal, including a human,
related to supranormal intracellular enzyme activity, which
comprises administering to a mammal having such condition or
disease, a pharmaceutically acceptable cell membrane permeable
prodrug, the prodrug being a covalent conjugate of a
pharmacologically active compound and an intracellular transporting
adjuvant, characterized by the presence of a covalent bond which is
scission-sensitive to intracellular enzyme activity, such that the
bond is broken in response to such activity, whereby the
pharmacologically active compound accumulates selectively within
cells having supranormal intracellular enzyme activity, or in their
immediate environment. In one particular aspect, the technique or
method is used to treat, e.g., a human patient.
In yet another aspect, the invention provides pharmaceutical
compounds for treating a condition or disease in a mammal related
to supranormal intracellular enzyme activity, by selectively
accumulating a pharmacologically active compound within cells
having such activity, comprising a pharmaceutically acceptable cell
membrane permeable prodrug, which is a covalent conjugate of the
pharmacologically active compound and an intracellular transporting
adjuvant, and is characterized by the presence of a covalent bond
which is scission-sensitive to intracellular enzyme activity, such
that the bond is broken in response to such activity. In one
particular aspect, the pharmaceutical compounds are used to treat,
e.g., a human patient.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 presents the proportion of cells with elevated intracellular
calcium levels in lymphocytes from a healthy individual and an
asthmatic patient, and the effects of Prodrug 1 on these clacium
levels, in comparison to treatment with BAPTA, before (Panel A) or
after (Panel B) IgE stimulation;
FIG. 2 compares cumulative mortality, with elapsed time (in hours),
in a rat model of permanent cerebral ischemia in the presence
(square) or absence (circle) of DP16.
FIG. 3 illustrates the dose-response curve for protection afforded
by DP16 against generalized epileptic seizures induced by
pilocarpine;
FIG. 4 illustrates the dose-response curve for protection afforded
by DP16 against pilocarpine induced fatal epileptic events;
FIG. 5 illustrates the dose-response curve for protection afforded
by DP16 in a metrazol minimum seizures test;
FIG. 6 illustrates results of experiments in hypoxia-reperfusion
cardiopathology. The upper panel (1) shows an EKG of a heart during
cardiac perfusion, the middle panel (2) shows an EKG of a heart
during low flow perfusion, with and without 1 .mu.g/L DP16
treatment and the lower panel (3) shows an EKG of a heart after
reperfusion with and without 1 .mu.g/L DP16 treatment.
FIG. 7 presents the superior protection of DP16 compared to
BAPTA-AM in hypoxia-reperfusion induced cardiopathology;
FIG. 8 presents the dose response curve of TVA compared to valproic
acid itself.
DETAILED DESCRIPTION OF THE INVENTION
Regulated activation of prodrugs by hyperactive intracellular
enzymes
According to the present invention, compounds are provided which
are cell permeable prodrugs, comprising a pharmacologically active
compound covalently bound to a lipophilic moiety which facilitates
intracellular transport of the prodrug. As used herein and in the
claims the term prodrug denotes a molecule which is incapable of
exerting the pharmacological activity of the active compound. The
active compound will exert its therapeutic effects after it is
released from the prodrugs of the invention by the action of
intracellular enzymes. The covalent bond of these prodrugs are
scission sensitive to enzymes that are hyperactive in the cells
that are affected, thereby providing selective activation of the
pharmacological compound in the diseased cells.
In certain preferred embodiments, the pharmacologically active
molecule may be a cell impermeable drug. In these embodiments
wherein the pharmacological compound is a cell impermeable drug,
the compound will be selectively accumulated in the affected
cells.
In other preferred embodiments, the pharmacological agents that are
incorporated into the prodrugs of the invention, are themselves
cell permeable molecules. In these embodiments the regulated
activation of the active compound is achieved in those cells that
require treatment, thereby significantly improving the therapeutic
index of the pharmacological agent.
Different types of intracellular enzyme systems that are
significantly elevated in pathological conditions may be used
according to the present invention, to achieve the preferential
release of the active drug compound within the diseased cells.
Suitable enzymes that are to be utilized according to the present
invention to activate the prodrugs include but are not limited to
lipases, proteases or glycosidases. Members of these classes of
enzymes are known to be elevated in a variety of diseases and
disorders.
In currently preferred embodiments, the enzymes that activate the
prodrugs are intracellular lipases. In most preferred embodiments
the covalent bond of the prodrug is scission sensitive to
phospholipases, a non limiting example of which are the
phospholipases A2.
Distinction among the various phospholipases is based in part on
their substrate specificity as well as their tissue localization,
regulation and physicochemical attributes. The different
specificities of these classes of phospholipases can serve as the
basis of designing prodrugs which undergo specific activation, as
suitable for the pathology to be treated.
The cleavage sites of the various phospholipases are herein
depicted schematically in the following scheme. ##STR1##
Prodrugs designed as substrates for phospholipase C (PLC) will much
more useful for treatment of chronic excitatory disorders such as
epilepsy. In this type of disorder PLC is involved in the earliest
events of hyperactivation (preceding the physiological attack),
while PLA.sub.2 activation coincides with epileptic seizures.
Prodrug activation by PLC could be most preferred for targeting of
antiepileptic drugs. Whereas prodrug activation by Phospholipase D
(PLD) could by appropriate for targeting of antitumor drugs. In
such prodrugs the P--O bond constituting the bond between the drug
and the phospholipid would be scission-sensitive to enzyme PLD,
thus releasing the antitumor agents intracellularly, and
accumulating these inhibitors in cells having a supranormal level
of PLD.
Phospholipases A.sub.2 are a family of esterases that hydrolyze the
sn-2 ester bonds in phosphoglyceride molecules releasing a free
fatty acid and a lysophospholipid. Classification of the members of
this family of enzymes is based on certain structural features
and/or their localization in different cells and tissues. In
principle, these enzymes are more active on aggregated phospholipid
substrates compared with monomeric soluble substrates.
Phospholipid conjugates of drugs that will be cleaved by
Phospholipases A.sub.2 have previously been disclosed either a) to
enhance penetration into cells; b) to enable formulation of drugs
in liposomes; or c) as a form of "enterocoating" that prevents
exposure of the gastric mucosa to the drug.
None of the previously disclosed uses of phospholipid-drug
conjugates is an essential feature of the present methods of using
these prodrugs, inasmuch as a) the present invention is effective
even with drugs that are already capable of penetrating cells, as
in the example of antiepileptic drugs; b) it is not desirable
according to the current invention to formulate the prodrugs into
liposomes since this achieves preferential distribution to specific
organs (e.g., the liver) or to specific cell types(e.g.,
macrophages) rather than to diseased cells within an organ or cell
population; c) the prodrugs according to the present invention are
intended for parenteral administration in order to prevent their
premature digestion by phospholipases in the digestive tract.
The prodrugs according to the present invention are contemplated to
be useful in the treatment of patients in both human and veterinary
medical practice. The prodrugs can be administered to a patient in
need thereof by any of the conventional parenteral routes of
administration, as may be appropriate for use in conjunction with
the selective activation afforded by the prodrugs according to the
invention for the disease or condition to be treated. These routes
include, but are not limited to, intravenous (i.v.) injection,
intramuscular (i.m.) injection, subcutaneous (s.c.) injection,
infusion into a body cavity, cerebrospinal injection, localized
infiltration into a target tissue, buccal absorption, and aerosol
inhalation, in an amount effective to treat the disease or
disorder. Formulations of the compounds of the present invention
into pharmaceutical compositions suitable for the chosen route of
administration may include any physiologically acceptable
solutions, suspensions, emulsions, microemulsions, micellar
dispersions, or the like, with any pharmaceutically acceptable
excipients, as are known in the art. In addition, formulations may
include various encapsulations or depots designed to achieve
sustained release of the prodrug, as in those circumstances where a
chronic disorder is to be treated.
According to one preferred embodiment of the present invention,
protease inhibitors are provided which comprise a peptide or
peptide analog which is a potent protease inhibitor, covalently
bound to a phospholipid. These prodrugs are cell permeable
molecules which are scission sensitive to abnormally hyperactivated
phospholipases. Preferred protease inhibitors may inclue peptides,
peptide analogs, or peptidomimetics.
A non-limiting example of such protease inhibitors are inhibitors
of the neutral calcium-activated protease Calpain. Excessive
activation of calpain may play a major role in a variety of
disorders, including cerebral ischemia, muscular dystrophy and
platelet aggregation (for review see Wang and Yuen, TIPS 15,
412-419, 1994). However, there are at present no selective and cell
permeable calpain inhibitors. The improvement according to the
present invention may be achieved with any of the known peptide or
peptide analogs that are known calpain inhibitors, such as those
reviewed by Wang and Yuen (ibid).
Within the scope of the present invention, additional embodiments
are provided wherein the covalent bond of the prodrug, comprising
said protease inhibitor, is scission sensitive to hyperactive
intracellular proteases. Such further embodiments have a scission
sensitive peptide bond between the protease inhibitor and a
lipophilic carrier, thereby releasing the inhibitor in those cells
that possess hyperactive protease activity. The use of lipophilic
carriers to facilitate transport of peptide analogs across
lipophilic barriers such as the blood brain barrier has been
disclosed for instance in International patent application
PCT/US93/09057. However, it is neither taught nor suggested in such
disclosures that lipid conjugates may be utilized to achieve
intracellular activation of a peptide drug.
In yet another embodiment, activation of the prodrugs is regulated
by enzymes which are intracellular glycosidases, a non-limiting
example of which is heparanase. Interaction of circulating cells of
the immune system, as well as platelets, with the subendothelial
extracellular matrix is associated with degradation of heparan
sulfate by the specific endoglycosidase, heparanase. This enzyme is
released from intracellular compartments in response to activation
signals, implicating its involvement in inflammation and immunity.
In contrast, various tumor cells express heparanase in a
constitutive manner, in correlation with their metastatic
potential. This enzyme is a suitable candidate for achieving
regulated activation of antitumor drugs, or of drugs that modulate
the immune response.
Prodrugs activated by phospholipases
The pharmacologically active compound may be by way of example a
pharmacologically active carboxylic acid, when the adjuvant may
comprise for example at least one pharmaceutically acceptable
alcohol which is selected from glycerol, C.sub.3-20 fatty acid
monoglycerides, C.sub.3-20 fatty acid diglycerides,
hydroxy-C.sub.2-6 -alkyl esters of C.sub.3-20 fatty acids,
hydroxy-C.sub.2-6 -alkyl esters of lysophosphatidic acids,
lyso-plasmalogens, lysophospholipids, lysophosphatidic acid amides,
glycerophosphoric acids, lysophophatidal-ethanolamine,
lyso-phosphatidylethanolamine and N-mono- and
N,N-di-(C.sub.1-4)-alkyl and quaternary derivatives of the amines
thereof.
Exemplary of pharmacologically active carboxylic acids are
branched-chain aliphatic carboxylic acids (e.g. valproic acid),
salicylic acids (e.g. acetylsalicylic acid), steroidal carboxylic
acids (e.g. lysergic and isolysergic acids), monoheterocyclic
carboxylic acids (e.g. nicotinic acid) and polyheterocyclic
carboxylic acids (e.g. penicillins and cephalosporins). While
pharmacologically active carboxylic acids are particularly
described herein, as exemplary of the active compounds which may be
conjugated with an intracellular transporting adjuvant, the
invention is not limited thereto. Thus, by way of further example,
it is entirely within the concept of the present invention to
conjugate therapeutically active nucleic acid (including RNA and
DNA) or fragments thereof with an intracellular transporting
adjuvant.
In a preferred embodiment, the prodrug according to the invention
comprises a conjugate of a calcium chelating agent and a lipid, and
may thus be of potential use for treating diseases or conditions
which are related to an unduly high level of intracellular
Ca.sup.2+ ions.
In a most preferred embodiment, the prodrug contains at least one
covalent bond between the pharmacologically active compound and the
intracellular transporting adjuvant, which covalent bond is
scission-sensitive to intracellular enzyme activity, with the
consequence that the greater part of the prodrug molecules will
move freely in and out of normal cells without scission of such
bond, whereas in the cells possessing the supranormal enzyme
activity only, the scission-sensitive bond in a high proportion of
prodrug molecules entering the cells will break. In those
embodiments where the pharmacologically active compound is cell
membrane impermeable the drug released from the prodrug will
accumulate intracellularly, within the abnormal cells possessing
supranormal enzyme activity.
Persons skilled in the art will appreciate in what manner the
concept of the invention may be applied to conditions and diseases
which are not necessarily related to an intracellular excess of
calcium ions, so that in such other cases, the prodrug will
incorporate an active compound which is not a calcium chelator but
which will possess other desired pharmacological activity.
The prodrug which comprises a calcium chelating agent is, e.g., a
partially or totally esterified carboxylic acid, which is an ester
of:
(a) a pharmaceutically acceptable chelating agent for calcium
having the formula (HOOC--CH.sub.2 --).sub.2 --N--A--N--(--CH.sub.2
COOH).sub.2 where A is saturated or unsaturated, aliphatic,
aromatic or heterocyclic linking radical containing, in a direct
chain link between the two depicted nitrogen atoms, 2-8 carbon
atoms in a continuous chain which may be interrupted by 2-4 oxygen
atoms, provided that the chain members directly connected to the
two depicted nitrogen atoms are not oxygen atoms, with
(b) a C.sub.3-32 pharmaceutically acceptable alcohol containing 1-3
OH radicals (e.g. such a C.sub.3-6 alcohol, or e.g. a C.sub.7-32
secondary monohydric alcohol);
and salts with alkali metals of the partially esterified carboxylic
acids, as well as acid addition salts of such of the esterified
carboxylic acids as contain one or more potentially salt-forming
nitrogen atoms.
The choice of the preferred alcohol that is appropriate for any
given prodrug is dependent on the intended therapeutic use of the
conjugate. Thus alcohols below C.sub.10 exhibit very low substrate
specificity, whereas alcohols above C.sub.12 or C.sub.14 are very
good substrates for the phospholipases and will therefore be
readily activated. Regulated activation will best be achieved by
the intermediate length alcohols such as C.sub.2 -C.sub.10, and
these will be preferred for the treatment of persistent or chronic
disease states or disorders.
In contradistinction, in certain disease states that require the
rapid release of the active agent the most preferred alcohols will
be the longer chain alcohols. This is most suitable for conditions
involving acute onset pathology such as in the treatment of
epilepsy with the prodrugs of the invention. Further, in the case
where there are relatively minimal differences in intracellular
enzymatic activity between normal and diseased or disordered cells,
relatively shorter chain alcohols may be selected.
The ester of choice may be one in which the linking radical A is a
member selected from the group consisting of --(CH.sub.2
CH.sub.2).sub.m -- where m=1-4, in which 2-4 of the carbon atoms
not attached to nitrogen may be replaced by oxygen atoms, and
--CR.dbd.CR--O--CH.sub.2 CH.sub.2 --O--CR'.dbd.CR'--, where each of
the pairs of radicals R--R and R'--R', together with the attached
--C.dbd.C-- moiety, complete an aromatic or heterocyclic ring
containing 5 or 6 ring atoms, the ring completed by R--R being the
same as or different from the ring completed by R'--R'.
In particular embodiments, the linking radical A may be, e.g.,
selected from --CH.sub.2 CH.sub.2 -- and --CH.sub.2 CH.sub.2
--O--CH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.2 --; or it may be e.g.
--CR.dbd.CR--O--CH.sub.2 CH.sub.2 --O--CR'.dbd.CR'--, where each of
the pairs of radicals R--R and R'--R', together with the attached
--C.dbd.C-- moiety, complete an aromatic or heterocyclic ring which
is selected from the group consisting of furan, thiophene, pyrrole,
pyrazole, imidazole, 1,2,3-triazole, oxazole, isoxazole, 1,2,3-
oxadiazole, 1,2,5-oxadiazole, thiazole, isothiazole,
1,2,3-thiadiazole, 1,2,5-thiadiazole, benzene, pyridine,
pyridazine, pyrimidine, pyrazine, 1,2,3-triazine, 1,2,4-triazine,
and 1,2-, 1,3- and 1,4-oxazines and thiazines, the ring completed
by R--R being the same as or different from the ring completed by
R'--R'. In a particularly preferred embodiment, the linking radical
A is --CR.dbd.CR--O--CH.sub.2 CH.sub.2 --O--CR'.dbd.CR'--, where
each of the pairs of radicals R--R and R'--R', together with the
attached --C.dbd.C-- moiety, completes the same or different rings
selected from unsubstituted and substituted benzene rings, in which
substituted benzene rings contain 1-4 substituents selected from
the group consisting of C.sub.1-3 -alkyl, C.sub.1-3 -alkoxy, F, Cl,
Br, I and CF.sub.3, or a single divalent substituent which is
--O--(CH.sub.2).sub.n --O-- and n=1-3.
It is presently preferred that the calcium chelating agent
incorporated in the prodrug is selected from
ethylene-1,2-diamine-N,N,N',N'-tetra-acetic acid,
ethylene-1,2-diol-bis-(2-aminoethyl ether)-N,N,N',N'-tetraacetic
acid and 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic
acid.
As mentioned above, C.sub.3-32, e.g. C.sub.3-6, alcohol referred to
above contains 1-3 OH radicals. When 2 OH radicals are present, one
of them may be esterified or otherwise derivatized, and when 3 OH
radicals are present, either 1 or 2 of the OH radicals may be
esterified or otherwise derivatized. Any carbon atoms in the
esterifying or otherwise derivatizing group(s) are not counted for
the purpose of the e.g. 3 to 6 carbon atoms which may be contained
in the pharmaceutically acceptable alcohols.
Thus, these alcohols may comprise, e.g., at least one member of the
group consisting of glycerol, C.sub.3-20 fatty acid monoglycerides,
C.sub.3-20 fatty acid diglycerides, hydroxy-C.sub.2-6 -alkyl esters
of C.sub.3-20 fatty acids, hydroxy-C.sub.2-6 -alkyl esters of
lysophosphatidic acids, lysoplasmalogens, lysophospholipids,
lysophosphatidic acid amides, glycerophosphoric acids,
lysophophatidalethanolamine, lysophosphatidylethanolamine and the
N-mono-C.sub.1-4 -alkyl, N,N-di-C.sub.1-4 -alkyl and quaternary
ammonium derivatives of such of the foregoing as are amines. An
example of a C.sub.7-32 secondary alcohol is 1-myristylmyristyl
alcohol.
The person skilled in the art will appreciate that the prodrug of
the present invention can be tailored in such a manner that the
desired pharmacologically active entity is released by action of
the specific enzyme known to be the source of enzyme hyperactivity
in the condition or disease being treated. For example,
membrane-associated calcium-independent plasmalogen-selective
PLA.sub.2 activity has been found to increase over 400% during two
minutes of global ischemia (P<0.01), was greater than 10-fold
(near to the maximum) after only five minutes of ischemia, and
remained activated throughout the entire ischemic interval examined
(up to 60 minutes), see Ford et al, J. Clin. Invest., 1991, 88(1):
331-5. These facts suggest attaching the pharmacological active
entity to the 2-position in a glycerophosphoric acid derivative,
and that use of a lysoplasmalogen may possibly be more effective as
the intracellular transporting adjuvant, to which the active entity
is attached covalently, than a lysophospholipid.
Many events (e.g. cytotoxic chemicals, physical stimuli and
infective agents) causing damage of the cell membrane can trigger a
cascade leading ultimately to a condition which mimics ischemic
damage(Robbins et al, Pathological Basis for Disease, 1984, p. 10,
W. B. Sanders Co.). The present invention will potentially be of
use for protecting cells in these circumstances, by introduction of
a calcium chelator intracellularly.
In this connection, it is noted that the antitumor drug Adriamycin,
which has been reported to inhibit Na--Ca exchange and to overload
the sarcoplasm with calcium, could induce contractile heart
failure; this would be consistent with the hypothesis that calcium
overload, in absence of ischemia, can leave behind long-lasting
contractile dysfunction (Kusuoka et al, J. Cardiovasc. Pharmacol.,
1991, 18(3): 437-44).
As indicated above, the concept of the present invention is not
restricted to the treatment of conditions or diseases related to
the intracellular level of Ca.sup.2+ ions, so that the materials
used in practicing the invention are not restricted to calcium
chelators. Thus for example, the pharmacologically active compound
may be e.g. an antiepileptic compound such as valproic acid.
In this connection, it is contemplated that application of the
present invention in this embodiment would enable a much lower
effective dose of valproic acid to be used than is otherwise the
case, thus potentially substantially reducing the occurrence of
undesired side-effects. In principle, any of the range of alcohols,
and examples thereof, mentioned above in connection with
esterification of calcium chelators may also be applied to the
esterification of valproic acid in accordance with the concept of
the present invention.
In a non-limiting embodiment, valproic acid may be esterified with,
e.g., 1-heptanoyl-sn-glycero-3-phosphorylcholine.
In another particular embodiment, the pharmacologically active
compound incorporated in the prodrug of the invention is a protein
kinase inhibitor. Where the protein kinase inhibitor is a
carboxylic acid, the prodrug may be e.g. an ester thereof with a
pharmaceutically acceptable alcohol such as glycerol, C.sub.3-20
fatty acid monoglycerides, C.sub.3-20 fatty acid diglycerides,
hydroxy-C.sub.2-6 -alkyl esters of C.sub.3-20 fatty acids,
hydroxy-C.sub.2-6 -alkyl esters of lysophosphatidic acids,
lysoplasmalogens, lysophospholipids, lysophosphatidic acid amides,
glycerophosphoric acids, lysophophatidalethanolamine,
lysophosphatidylethanolamine and N-mono- and
N,N-di-(C.sub.1-4)-alkyl and quaternary derivatives of the amines
thereof. Such a carboxylic acid is e.g. protein kinase inhibitor
K252b from Nocardiopsis sp.
Where the protein kinase inhibitor contains an amine group with a
replaceable N-linked hydrogen atom, the prodrug may be e.g. an
amide thereof with a phosphoric acid derivative selected from
glycerophosphoric acids, O-acylated or etherified glycerophosphoric
acids, and monoacylated monoetherified glycerophosphoric acids.
Such protein inhibitors are e.g. isoquinoline-5-sulfonamide
N-substituted by an acyclic or heterocyclic aminoalkyl radical such
as NHCH.sub.2 CH.sub.2 NHCH.sub.3 and 2-methylpiperazin-1-yl. Where
the protein kinase inhibitor contains at least one phenolic hydroxy
group, the prodrug may be e.g. an ester thereof with a phosphoric
acid derivative selected from glycerophosphoric acids, O-acylated
glycerophosphoric acids, etherified glycerophosphoric acids, and
monoacylated monoetherified glycerophosphoric acids. Such a protein
kinase inhibitor is e.g. 4',5,7-trihydroxyisoflavone.
In another particular embodiment, the pharmacologically active
compound incorporated in the prodrug of the invention is an
antitumor agent. The ordinary artisan will understand that the
principle of the invention can be applied to any suitable antitumor
agent by linking such an agent to an intracellular transporting
adjuvant as described above, to which the pharmacologically active
compound is attached covalently. The linkage is selected so that
supranormal intracellular enzyme activity characteristic of target
cells (e.g., tumor cells) will cleave the intracellular
transporting adjuvant from the pharmaceutically active compound. In
a particular aspect,the antitumor agent is, for example, a folic
acid agonist such as a 4-amino analog of folic acid. A
representative member of this class of compounds is methotrexate.
Methotrexate and related compounds are known to the art as
effective antitumor agents that have also been used in the
treatment of psoriasis and in the modulation of cell mediated
immunity. Impaired transport of methotrexate into target cells is
believed to be one mechanism for the development of tumor
resistance to that drug (Goodman and Gilman's, THE PHARMACOLOGICAL
BASIS OF THERAPEUTICS, 8Th Ed., 1990, Pergamon Press, hereby
incorporated by reference in its entirety). Thus, methotrexate
linked to a cell membrane permeable adjuvant cleavable by
supranormal intracellular enzyme associated with a diseased or
disordered target cell will enhance the specificity and
effectiveness of such treatment of tumor cells by antitumor drugs,
such as, e.g, methotrexate or other folic acid antagonists. Prodrug
derivatives of methotrexate are also contemplated to be used to
treat any of the other aformentioned conditions treatable by
methotrexate
When selecting the intracellular transporting adjuvant for the
purposes of the present invention, the skilled person will of
course take into consideration the necessity for avoiding such
adjuvants, e.g. certain 1,2-diacylglycerols, which are activators
of protein kinase C (see Lapetina et al, J. Biol. Chem., 1985, 260:
1358 and Boynton et al, Biochem. Biophys. Res. Comm., 1983, 115:
383), or intracellular transporting adjuvant which are likely to
give rise to undesirable products such as these in the cell. In
addition, the artisan will appreciate that the selected linker to
the intracellular transporting adjuvant should be selected to avoid
interaction with desired pharmacological activity and to avoid
rapid, nonspecific intracellular degradation after specific
cleavage.
The following examples are to be construed in a non-limitating
fashion and represent certain preferred embodiments of the
invention. One skilled in the art can readily devise many
variations and modifications of the principles disclosed herein
without departing from the scope of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following examples illustrate various aspects of the present
invention and are not to be construed to limit the claims in any
manner whatsoever
EXAMPLES
Example 1
Preparation of Esters of Heptanoyl-sn-3-glycero-phosporylcholine
(Prodrug-1 and Prodrug-2).
Introduction
"Prodrug-1" is the name used herein to denote a 1:1 ester of
1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)
with the choline derivative ROCH.sub.2 --CH(OH)-CH.sub.2
O--(PO.sub.2)--OCH.sub.2 N.sup.+ (CH.sub.3).sub.2, wherein R is
heptanoyl. BAPTA is a caldium chelator, to which the human cell
membrane is normally impermeable, whereas the cell membrane is
permeable to prodrug-1, which is not a calcium chelator per se. The
carboxylic ester links in prodrug-1 are digestible by PLA.sub.2, so
that activated cells such as IgE lymphocytes should exhibit a
selective intracellular accumulation of BAPTA, compared to the
unactivated cells, with the result that the [Ca.sup.2+ ].sub.i
level in the activated cells should be reduced when compared with
unactivated cells. "Prodrug-2" is the 1:2 ester of BAPTA with the
depicted choline derivative.
Procedure
(a) Diheptanoyl-L-.alpha.-lecithin
In a dry 3-neck 500 ml flask equipped with oil-sealed stirrer,
CaCl.sub.2 tube and dropping funnel, were placed 100 ml of 5 mm
diameter glass beads and 11.0 g (0.01 mole) of CdCl.sub.2 adduct of
synthetic L-.alpha.-glycero-phosphorylcholine. The flask was
immersed in an ice-water bath, and to the rapidly-stirred mixture
there was added a thin stream of 29.7 g (0.2 mole) freshly prepared
heptanoyl chloride dissolved in 60 ml chloroform, followed by 11 ml
(0.14 mole) anhydrous pyridine dissolved in 100 ml
chloroform(anhydrous, alcohol-free). After 30 minutes, the bath
temperature was raised to 25.degree. C. and stirring continued for
2 hours. The reaction mixture was poured through a filter-less
Buchner, the glass beads washed with 3.times.50 ml chloroform and
the combined filtrates clarified by centrifugation. The supernatant
was concentrated under reduced pressure, the residue kept for
several hours at 0.1 mmHg vacuum and bath temperature 30-35.degree.
C. to remove most excess pyridine, and was then stirred with 500 ml
anhydrous acetone for 10 minutes, and centrifuged. The precipitate
was treated similarly with 2.times.100 ml anhydrous acetone and
2.times.100 ml anhydrous ether.
The residual solid material was dried under reduced pressure and
freed of the last traces of cadmium chloride and pyridine
hydrochloride, by dissolving in 200 ml of a 5:4:1 by volume mixture
of chloroform/methanol/water, and passing the solution through a
120 cm long.times.2.5 cm diameter column containing an equivolume
mixture of Amberlites IR-45 and IRC-50. The column was washed with
500 ml of the same chloroform/methanol/water mixture, the combined
effluents were concentrated to dryness under reduced pressure from
a bath at 40-45.degree. C., and the residue dried at 0.1 mm vacuum
and 45.degree. C. The crude product was purified by precipitation
from a solution in 50 ml chloroform, with 150 ml acetone,
centrifugation and recrystallization of the precipitate, 2.3 g
(47.6%) from chloroform and ether. (Di-octanoyl-L-.alpha.-lecithin
can be prepared similarly.)
(b) 1-Heptanoyl-sn-3-glycerophosphorylcholine
A solution of the product of part (a) (1.2 mmol) in a mixture of
ether (196 ml) and methanol (12 ml) was stirred vigorously in
presence of (HOCH.sub.2).sub.3 C--NH.sub.2.HCl (50 ml of 0.1 M, pH
8.7) containing CaCl.sub.2 (0.72 mM) and 5 mg of crude rattle snake
venom (Crotalus adamanteus) as a source of phospholipase A.sub.2,
at 37.degree. C. for 3 hours. The reaction was monitored by TLC
(70:25:4 by volume chloroform/methanol/water). After completion of
reaction, the organic layer was separated, and the aqueous layer
was washed with ether and then lyophilized. The residue was
extracted with 2:1 by volume chloroform/methanol and centrifuged.
On evaporation of the clear supernatant, the title product was
obtained in 90% yield. Thin layer chromatography using 70:25:4 by
volume chloroform/methanol/water showed that it was free from
starting material and heptanoic acid. Any fatty acid in the product
can however be remove by crystallization from ethanol-ether.
Note: this is a general method for scission of the glycerol-2-ester
bond. (Octanoyl-sn-3-glycerophosphoryl-choline can be prepared
similarly.)
(c) Prodrug-1 and Prodrug-2
A solution of the product of part (b) (0.5 g, 1.04 mmol) in
chloroform (15 ml, freshly distilled over P.sub.2 O.sub.5) was
added to a solution of BAPTA (0.495 g, 1.03 mmol for the monoester
Prodrug-1, or 0.248 g, 0.51 mmol for the diester Prodrug-2),
N,N'-dicyclohexyl-carbodiimide (0.214 g, 1.03 mmol) and
4-dimethylaminopyridine (0.025 g, 0.202 mmol) and HCONMe.sub.2 (20
ml, freshly distilled over CaH.sub.2) under a nitrogen atmosphere,
and the mixture was stirred at room temperature for two days. The
reaction was monitored by TLC (65:35:5 by volume
chloroform/methanol/water).
The precipitate was removed by filtration, the filtrate was
concentrated by evaporation in vacuo at 35.degree. C. and the
residue was dissolved in 2:1:2 by volume
chloroform/isopropanol/water). The organic layer was separated,
dried (Na.sub.2 SO.sub.4) and then passed through a 20 cm
long.times.1.8 cm diameter column of silicic acid (Bio-Sil-HA). The
column was thoroughly washed with chloroform until free from BAPTA
(TLC) and then eluted with a gradient of chloroform/methanol (1:1
by volume) to pure methanol, the elution being monitored by TLC.
The eluted fractions were combined and concentrated by evaporation.
The desired title product (i.e. Prodrug-1 or Prodrug-2, depending
on the number of molar equivalents of BAPTA used) was crystallized
from ether and dried in vacuo over P.sub.2 O.sub.5 at 30.degree.
C.: yield 0.3 g (30%).
It will be apparent that the corresponding triester or tetraester
may be obtained by varying appropriately number of molar
equivalents of BAPTA. (The analogous octanoyl esters are prepared
similarly.)
Example 2
Application of Prodrug-1 for reduction of the intracellular calcium
level in hyperactivated cells.
Method
Intracellular free [Ca.sup.2+ ].sub.i content was monitored by flow
cytometry using the Ca.sup.2+ -sensitive dye fluo-3/AM (Molecular
Probe Inc., OR)(Minta, Kao and Tsien, 1989, J. Biol. Chem.
264:8171-8178). Cells obtained from donor blood and those from the
blood of an asthmatic patient were further washed twice in DMEM and
resuspended to a concentration of 10.sup.7 cells/ml. Fluo-3/AM (1
mM) was prepared in DMSO augmented with the nonionic surfactant
Pluronic F-127 (Wyandotte Corp., MI). Aliquots of fluo-3/AM stock
solution were added to cell suspensions in DMEM/HEPES at a final
concentration of 3 .mu.M (loading buffer). Loading was allowed to
proceed for 30 min. at 37.degree. C. and continued for 1 hour at
23.degree. C. with gentle agitation. Cells were then adjusted to
desired concentrations using fresh DMEM/HEPES, supplemented with 2%
horse serum. Autofluorescence was eliminated by setting the
threshold sensitivity above the levels obtained in absence of dye.
Fluorescence intensity data was collected from 5000 single cells
and values were expressed as arbitrary fluorescence units.
Prodrug-1 (1 mM) was prepared in DMSO and added when appropriate at
a final concentration of 3 .mu.M to the cells for 5 min. prior to
calcium treatment.
Results
Lymphocytes from donor blood and from the blood of an asthmatic
patient were exposed to prodrug-1. Accumulation of the liberated
BAPTA chelator within the cell was estimated by measurement of
[Ca.sup.2+ ].sub.i, by flow cytometry using fluo-3/AM as described
above. The results are presented in FIG. 1, in which the [Ca.sup.2+
].sub.i levels are shown as follows:
Panel A presents a comparison between the lymphocytes isolated from
a healthy domor and those of the asthmatic patient, in terms of the
proportion of cells having high intracellular free calcium.
Panel B presents a comparison of the same cell populations after
stimulation with IgE. As shown in panel B, the prodrug also
provides protection against high intracellular calcium in IgE
stimulated cells.
It was found that lymphocytes from an asthmatic patient have a dual
partition according to the [Ca.sup.2+ ].sub.i level. About 50% of
the cells exhibit a high [Ca.sup.2+ ].sub.i level indicating cell
hyperactivation (panel A), while the second part of the population
is similar to the normal one. In the case where the cells have been
treated with prodrug-1, the population of hyperactivated cells is
back to normal, while the population of non-activated cells remains
unchanged. These data demonstrate that prodrug-1 provides selective
accumulation of the chelator within activated, but not in
non-activated cells. BAPTA itself, which is a cell impermeable
molecule is ineffective in reducing the intracellular calcium
levels, in either stimulated or untreated cells.
Example 3
Prodrugs of potential application in the treating tumors.
Introduction
In this Example, there are presented a number of illustrative
embodiments of the present invention in which a prodrug comprises a
protein kinase inhibitor. After administration of the prodrug, the
inhibitor would be accumulated in a cell exhibiting abnormal
proliferation, thus providing potentially an important tool for use
in antitumor therapy.
(i) The compound QSO.sub.2 N where Q=5-isoquinolyl and NN
=NHCH.sub.2 CH.sub.2 NHCH.sub.3, is a selective inhibitor of
cAMP-dependent protein kinase: Hidaka et al, Biochemistry, 1984,
23: 5036, and Tash et al, J. Cell Biol., 1986, 103: 649. Similarly,
the compound QSO.sub.2 N where Q=5-isoquinolyl and
N=2-methylpiperazin-1-yl, is a potent inhibitor of cyclic
nucleotide dependent protein kinase and protein kinase C: Hidaka et
al, loc cit, and Kikuchi et al, Nucl. Acid Res., 1988, 16: 10171.
These compounds can be covalently conjugated to an intracellular
transporting adjuvant by methods known to persons of the art, e.g.
illustratively: ##STR2##
In scheme (b), R is an aliphatic hydrocarbon group such as is found
in plasmalogens (or it may be inserted in a conventional synthetic
procedure) and A is an aliphatic acyl radical, e.g. lauroyl,
myristoyl, palmitoyl, stearyl and oleyl.
The compound QSO.sub.2 NN where Q=5-isoquinolyl and NN
=2-methylpiperazin-1-yl, may be attached in a similar manner by
means of the piperazine N.sup.4 atom.
It would be expected that the P--N bond in prodrugs (A) and (B)
depicted above would be scission-sensitive to enzyme PLD, thus
releasing the described protein kinase inhibitors intracellularly,
and accumulating these inhibitors in cells having a supranormal
level of PLD.
(ii)4',5,7-trihydroxyflavone is an inhibitor of tyrosine specific
protein kinase: Akiyama et al, J. Biol. Chem., 1987, 262: 5592.
This compound can be conjugated to an intracellular transporting
adjuvant by methods (a) and (b) described in part (i), above. The
illustrative conjugates would have structures (C) & (D):
##STR3## where R' and A have the meanings given above and Q' is the
residue of 4',5,7-trihydroxyisoflavone from which one phenolic
hydrogen atom has been removed and which is thus attached to the
rest of the molecule by an O atom forming a P--O bond. It would be
expected that this P--O bond in prodrugs (C) and (D) depicted above
would be scission-sensitive to enzyme PLD, thus releasing the
described protein kinase inhibitors intracellularly, and
accumulating these inhibitors in cells having a supranormal level
of PLD.
(iii) Protein kinase inhibitor K252b from Nocardiopsis sp. is a
carboxylic acid believed to have the following formula:
##STR4##
This compound can be conjugated to an intracellular transporting
adjuvant, e.g., by the method described in Example 1, above.
Exemplary conjugates are esters of the carboxylic function in the
above formula, with e.g. heptanoyl-sn-3-glycerophosphoryl-choline
or octanoyl-sn-3-glycerophosphoryl-choline.
Example 4
Preparation and biological properties of DP16.
4.1) Preparation of DP16
"DP16" denotes herein to denote a 1:1 ester of BAPTA with the
phosphorylcholine derivative ROCH.sub.2 --CH(OH)--CH.sub.2
O--(PO.sub.2)--OCH.sub.2 N.sup.+ (CH.sub.3).sub.2, where R is
hexadecanoyl. DP16 was prepared according to the method described
in Example 1.
4.2) DP16 testing in models of brain ischemia
a) Permanent ischemia model in rats:
Bilateral ligation of the common carotid arteries is the simplest
and most direct approach for inducing permanent partial ischemia.
In the rats there is almost 64% mortality 24 h later. The causes of
mortality are largely brain swelling (edema) and focal lesions
(infarcts). Permanent partial global is achieved by isolation of
the common carotid artery through an incision on the ventral
surface of the neck. The salivary glands are moved laterally and
the carotid sheath exposed. Both the vagus and sympathetic nerves
are separated from the common carotid artery, which is then
permanently ligated. Sprague-Dawley rats (250-300 g) were
anesthetized with halothane or by intramuscular injection of 0.1 ml
Ketamine (0.1 g/ml, Parke Davis UK) and 0.1 ml Rompun (2%, Bayer,
FRG) per 300 g body weight. DP16 was administered intraperitoneally
(i.p., 0.001-0.1 mg/kg) when appropriate following the artery
ligation. Every experimental and control group included 14 male
rats. Statistical analysis was performed according to t-test
criteria.
b) Embolic stroke:
Sprague-Dawley rats (300 g) are anesthetized with halothane. The
right common carotid artery is exposed and the external carotid and
pterygopalatine arteries are ligated with No. 0 silk thread. The
common carotid artery is cannulated with a plastic tube previously
filled with heparinized saline. The cannula is then injected (0.5
ml gas-tight Hamilton syringe) with a suspension of polystyrene
spheres, followed by a flush of 0.5 ml saline. The common carotid
artery is then permanently ligated. The polystyrene 15 .mu.m
spheres are prepared in 0.05% Tween-80 in normal saline followed by
5 min. of full power sonication. A 100 .mu.l aliquot is taken and
immediately transferred to the syringe.
c) Ischemic fetal brain model:
Sprague-Dawley pregnant rats were used at 20 days gestation.
Animals were anesthetized by intramuscular injection of 0.1 ml
Ketamine (0.1 g/ml, Parke Davis, UK) and 0.1 ml Rompun (2%, Bayer,
FRG) per 300 g body weight. An abdominal incision was performed and
the two uterine horns were exposed and kept moist throughout the
surgery. Intracerebral injection of 1-2mCi/2 ml [.sup.3 H]
arachidonic acid (Na+, 240 mCi/mmol from New England Nuclear,
Boston, Mass.) and/or 1.5 mCi/2 ml [.sup.14 C] palmitic acid (Na+,
819 mCi/mmol from Amersham, Searle, UK) in isotonic salt solution
containing NaHCO.sub.3 (1.32 g %), into the embryos was performed
through the uterine wall into the fontanellae. Custom made syringes
(33 gauge, 0.375" length from Hamilton, Reno, Nev.) were used to
reduce brain edema. After injection fetuses were returned to the
abdominal cavity for maintenance at physiological temperature.
After 1 h they were subjected to blood flow restriction for 20 min.
(restriction session) by clamping the blood vessels in the placenta
manifold. Whenever desired, circulation was restored for 30 min. by
removal of the clamps (reperfusion session). At all times both
restricted and sham-operated fetuses were maintained in the
abdominal cavity before surgical delivery. After delivery through a
transverse cut in the uterus, viable fetuses with no apparent edema
were killed without delay and excised fetal brains were immediately
homogenized in suitable organic solvents for further treatment.
d) Fetal cerebral hemispheres model:
Rat fetuses were removed from the uterine horns in a viable state
and their cerebral hemispheres were dissected within 15 sec after
decapitation. The cerebral hemispheres freed of blood and meninges
were separated and each (50.+-.2.5.mg) was placed in a well of a
24-well Falcon culture dish. Tissue was quickly washed twice in
cold Dulbecco's Modified Eagle Medium (DMEM, Grand Island Biol.
Colo.) and then incubated at 37.degree. C. in 0.6-1.2 ml DMEM
flushed with oxygen and supplemented with various additives.
Aliquots of incubation medium (0.1 ml) were taken for eicosanoid
determination by a radioimmunoasay (RIA) technique. After
acidification with 5 ml formic acid, 0.1 ml of isopropanol and 0.5
ml diethylether were added. After mixing and low speed
centrifugation (2500.times.g, 5 min.) the organic layer was
collected and dried under a stream of nitrogen. The resulting
residue was dissolved in 0.1 ml sodium phosphate buffer pH 7.4,
containing 0.1% bovine serum albumin. Samples were incubated
overnight at 4.degree. C. with the appropriate polyclonal
antiserum, and .sup.3 H-labeled tracer (4000 cpm/tube) in a final
volume of 0.3 ml. Unbound material was precipitated with 0.3 ml
dextran-coated charcoal (Pharmacia, Sweden). After centrifugation
at 4.degree. C. aliquots of the supernatant (0.4 ml) were
transferred to vials and after addition of scintillation liquid
samples were counted in a Packard Tricarb scintillation counter.
[.sup.3 H] Arachidonic acid (240 Ci/mmol) (New England Nuclear,
Boston, Mass.) dissolved in isotonic NaHCO.sub.3 (1.32% w/v) was
injected through the uterine wall and the fontanellae into the
embryonic brain. After injection fetuses were returned to the
abdominal cavity for maintenance under physiological conditions.
After 1h, fetuses were delivered and immediately sacrificed.
Cerebral hemispheres were rapidly excised for subsequent ex vivo
incubation or for lipid extraction.
e) Results
Bilateral Permanent Cerebral Ischemia causes progressive loss of
experimental animals up-to 6-7 days after surgery. As illustrated
in FIG. 2, DP16 decreases post-ischemic mortality by 250%, compared
with control using non-protected rats (p<0.01). These data
demonstrate the potential ability of DP16 to treat otherwise fatal
ischemic conditions.
f) Heart ischemia-Langendorff perfused heart model:
White rats were sacrificed by cervical dislocation and their hearts
were rapidly removed and reperfused at 60 mmHg with modified
Krebs-Henselleit buffer utilizing a Langendorff perfused heart
model. Hearts were perfused for 10-min. preequlibration interval
and were subsequently rendered either global ischemic (zero flow)
or continuously perfused for the indicated time. Perfusion were
terminated by rapid excision of ventricular tissue and directly
submersion into cold homogenization buffer (10 mM imidazole, 10 mM
KCl, 0.25 M sucrose [grade 1], pH 7.8) Both the activation of
phospholipase A2 and its reversibility during reperfusion were
temporally correlated to alterations in myocytic anaerobic
metabolism and electron microscopic analyses.
g) Ventricular fibrillation model by coronary occlusion:
Dogs (11.6-20.7 kg) were anesthetized and connected to
instrumentation to measure left circumflex coronary blood flow,
left ventricular pressure, and ventricular electrogram. The left
anterior descending artery was ligated and an anterior wall
myocardial infarction was then produced. All leads to the
cardiovascular instrumentation were tunneled under the skin to exit
on the back of the animal's neck. Appropriate medicine was given to
minimize postoperative pain and prevent inflammation. The ischemia
test was performed after 3-4 weeks.
4.3) DP 16 testing in treatment of epileptic disorders:
a) Pilocarpine-based model of experimental epilepsy: Acetylcholine,
acetylcholinesterase inhibitors and acetylcholine analogues are
effective epileptogenic agents when applied intracerebrally or
systematically (see ref. in Leite et al., Neurosci. & Biobeh.
Rev., 1990, 14:511-17). It was demonstrated in different species
that systemic administration of muscarinic cholinergic agonists
produced electroencephalographic and behavioral limbic seizure
accompanied by widespread brain damage resembling topographically
that produced by kainic acid and folates and are frequently
observed in autopsied human epileptics. Systemic injections of the
pilocarpine, a potent muscarinic cholinergic agonist, are capable
of producing a sequence of behavioral alterations including
stirring spells, facial automatisms and motor limbic seizures, that
develop over 1-2 hours and build progressively into limbic status
and following by general status epilepticus.
b) Results
Immediately following injection of pilocarpine, akinesia, ataxic
lurching, facial automatism and heart tremor dominated the animals'
behavior. Further development of epileptic events is dose -
dependent. Administration of pilocarpine in doses of 300-350 mg/kg
causes appearance of limbic seizures with rearing, forelimb clonus,
salivation, intense masticatory jaw movements and falling. Motor
limbic seizures commenced after 20-30 min., recurred every 2-8 min
and lead to status epilepticus. Increase of the dose of pilocarpine
up-to 400 mg/kg abolished limbic seizures and after 15-25 min of
initial behavioral alterations causes fatal general tonic - clonic
convulsions. We consider this dose as the LD.sub.100.
Administration of DP16 prior to pilocarpine prevented death in the
animals and decreased epileptiform manifestations. As shown in FIG.
3, DP16 protected animals in a dose dependent fashion against
generalized epileptic events induced by pilocarpine. As shown in
FIG. 4, DP16 exhibits dose dependent therapeutic effects at doses
in the range 10.sup.-8 to 10.sup.-5 mg/kg, and decreased the
severity of the attacks as well, with a significant reduction in
fatal seizures. For this particular model of epilepsy (pilocarpine
400 mg/kg; rats) the estimated therapeutic index (ET) of DP16 is
0.5 mg/kg/5.times.10.sup.-7 mg/kg=1.times.10.sup.6. The data
obtained suggest that DP16 is an extremely promising prodrug for
the treatment of epileptic disorders.
c) Antiepileptic effects of DP16:
Metrazol minimal seizures test.
Testing of DP16 as a possible antiepileptic drug was performed on
3-4 week old male BALB/c mice (18-27 g). Animals were maintained on
an adequate diet and allowed free access to food and water except
briefly during the experimental period. Animals were separately
housed for one hour in transparent plastic cages before treatment
and during the experimental period. Drugs were dissolved in normal
saline with injection volume adjusted to 0.01 ml/g of body weight.
DP16 was administered i.p., in doses ranging from 0.1 to 300
.mu.g/kg: (0.1 .mu.g/kg: n=10, 5 .mu.g/kg: n=10, 25 .mu.g/kg: n=20,
75 .mu.g/kg: n=20, 150 .mu.g/kg: n=20, and 300 .mu.g/kg: n=10
animals respectively). Control animals received injections i.p. of
normal saline. DP16 or saline administration followed in 30 minutes
by Metrazol (50 .mu.g/kg, s.c.). Subsequently epileptic signs were
observed for the next 30 minutes. Absence or relative delay of
myoclonic jerks (MJ) in the experimental group was considered as
indication of possible antiepileptic activity. Data were subjected
to chi-square analysis with the computer statistic package
"StatViewII".
d) Results and Conclusions:
Metrazol in a dosage of 50 .mu.g/kg, s.c. caused myoclonic jerks
(MJ) in all of control mice with a latent period of 1011 min
(n=11). The effect of DP16 on the appearance of minimal metrazol
induced seizures is shown in FIG. 5. The doses are presented in
this figure in terms of mg/kg of the active pharmacological
component of the drug, i.e. BAPTA. Mice treated with 0.1 .mu.g/kg
DP16 showed the same response to metrazol as control (untreated)
animals. DP16 in doses ranging from 5 to 300 .mu.g/kg exhibited a
significant protective effect (p<0.001). The results of the test
suggest a significant dose-dependent antiepileptic effect of DP16
on the metrazol induced seizures.
4.4) Investigation of cardioprotective effect of DP16:
a) Ex-vivo rat heart Low-flow--Reperfusion model.
Method and Results
The following experiments demonstrate the protective effects of
DP16 in models of cardiac diseases. Low-flow Reperfusion
Langendorff's heart (Meely and Rovetto, 1975, METHODS IN
ENZYMOLOGY, v39:43-60) is an established ex vivo model of a human
ischemic heart. A severe decrease in perfusion pressure (PP) below
20 mm Hg (low-flow period) causes sinus bradycardia culminating by
stable AV block ("AVB"; 10 out of 11 hearts) frequently followed by
ventricular arythmia. Restoration of perfusion pressure causes
paraxysmal tachyarrhythmia followed by irreversable ventricular
fibrillation (VF).
The experiments were preformed ex vivo on 39 rat hearts. Heart
electrical activity and perfusion pressure were stable following 15
min., each. Perfusion buffer was supplemented with DP16 (1.0
.mu.g/l) following the stable AV block during low flow perfusion
and during the Reperfusion period.
Treatment of Cardiac Ischemia--Reperfusion with DP16.
The experimental protocol documented by FIG. 16 included peroiods
of Normal Coronary Flow (FIG. 6, NF, panel 1) followed by Low-Flow
(LF) and then by Normal flow-reperfusion (NF-Rp) (panels 2 and 3,
respectively).
The experiments were performed by addition of DP16 (0.5-500
.mu.g/l) to the perfusion buffer after AV block establishment. In
11 out of 16 experiments DP16 (1.0 .mu.g/l) to the perfusion buffer
caused complete restoration of AV synchronism and in the additional
5 cases it resulted in a decrease dlevel of AVB and prevented
ventricular fibrillation (FIG. 6). Moreover, DP16 showed notable
cardioprotective effects during the reperfusion period. Full
restoration of the sinum rhythm was observed in 11 out of 16
experiments.
Conclusion
Evaluation of the cardioprotective effect of DP16 in the Low
Flow-Reperfusion model as compared to treatment with parent
compound BAPTA and to cell permeable BAPTA derivative, BAPTA-AM
(supplied by Molectular Probes) and shown to have much better
efficiency in resolving atrio-ventricular blockade and preventing
ventricular fibrillation as indicated by FIG. 7.
b) DP16 prevents isoproterenol induced myocardial damage
Method and Results
Administration of the potent .beta.-adrenoreceptor agonist
isoproterenol (ISO) is commonly accepted model of experimental
myocardial pathology. The cardioprotective effect of DP16 was
tested on 82 Sprague-Dawley female rats weighing 250-350 g.
Myocardial damage was induced in rats by two consecutive injections
of ISO (85 .mu.g/kg, s.c.). When appropriate, the injections of ISO
were followed in 30 and 180 minutes by DP16 (0.01 .mu.g/kg, i.p.).
The effect of DP16 was estimated by ECG analysis and determination
of serum glutamate-oxaloacetate transaminase (SGOT) and
lactatdehydrogenase (LDH) activity. Mortality of control rats after
ISO intervention was 17.1.+-.5.9% (7 out of 41). The surviving
animals exhibited striking hyperacute deviation ST-segment in lead
1 and 2 ECG. Pathological signs on ECG were aggravated during the
experimental period. In 48 hours after the second ISO injection all
treated animals displayed pathological displacement of ST-segment..
Administration of DP16 decreased mortality in 2 cases (2 out of
30). Animals receiving DP16 exhibited significantly (p<0.05)
fewer alterations in the ECG. Pathological displacement of the
ST-segment was found only on 28 and 40% of ECG (in 24 and in 48
hours following ISO respectively). Biochemical determination
demonstrated a 1.7-1.9 fold increase if SGOT and LDH in ISO treated
control rats (p<0.05). Treatment with DP16 substantially
decreased the percentage of experimental animals exhibiting
abnormal level of SGOT and LDH activity.
Conclusions
The data above suggest a significant cardioprotective effect of
DP16 in an in vivo model of myocardial pathology.
c) Pilocarpine and cardiotoxicity.
Two types of death were found in rats treated with pilocarpine:
first death due to fatal convulsions and second, retarded death not
immediately due to epileptic events. We attempted to understand the
actual reason of retarded death of rats after pilocarpine-induced
convulsions. Under macroscopic autopsy of these animals signs of
cardiopulmonary damages were seen: lung edema and hemorrhages,
dilated and in same cases deformed hearts. Dyeing of hearts with
0.1% Trypan blue in surviving animals revealed spotted picture of
myocardia with areas of intensive dye absorption, i.e., damaged
parts, and pale areas, i.e., infarctions. Thus, we can consider
that after pilocarpine administration, there developed heart
damage, which we term post-pilocarpine--seizure-cardiopathy (PSCP).
Studies of PSCP in relation to DP16 evaluation were performed in
vivo and in vitro with rats which survived after convulsive and
sub-convulsive doses of Pilocarpine.
d) Post seizure cardiopathy (PSCP) model:
Adult (2-3 months) male Sprague-Dawley rats were used for all
experiments. They were fed with standard briquette chow with water
ad libitum and were maintained in standard plastic cages (4-5
individuals in each cage) under natural illumination. A
pilocarpine-scopolamine epileptic status model (pilocarpine) was
performed as described earlier. In a group of 23 rats, pilocarpine
was administered i.p. in different doses which ranged from 100 to
400 mg/kg body weight (B/W) for different periods of time; a second
group of 17 rats was treated with DP16 prior to pilocarpine
administration, wherein the DP16 was injected for 30 min before
pilocarpine in the next dose range and its effect was investigated
in the ensuing periods.
In vivo ECG (Birtcher-Cardio-Tracer, model 375, USA) in three
standard leads were recorded under ketamine anesthesia (3.3 mg/kg
Imalgene 100, Rhone Merieux, France and 7 mg/kg Rompun, Bayer
Leverkusen, Germany, i.m.). ECG recordings were made in the period
before pilocarpine injections (control), 24 h after pilocarpine
administration (acute period) and after relative stabilization of
cardiac function, on the 3-14th day after pilocarpine
administration. Part of the ECG recordings were made under nembutal
anesthesia (35 mg/kg, i.p.) in the period before establishing
Langendorff's perfusion isolated heart preparation.
Perfusion-Hypoxia-Reperfusion isolated heart model (PHR) was
performed with the conventional Langendorff technique
(non-recirculating perfusion system) adjusted to 37.degree. C. in
two modifications: 1. under constant Perfusion Pressure (PP)--60 mm
Hg; or 2. under constant flow, established after the first 10-15
min perfusion with PP as above, by adjusting flow with help of
peristaltic pump (Ismatec SA, Laboratoriumstechnic, Switzerland).
In the case of constant PP the volume of effluent flow was measured
on electron balance (Precisa 1000C-3000D, Switzerland). In case of
constant flow, established at the control period, flow did not
change during subsequent experimental periods and PP was recorded
frequently. After 30 min of the control period, perfusion was
stopped for 30 min and subsequent reperfusion period lasted 30 min.
Direct ECG were recorded from ventricular apex (lead 1), auriculum
(lead 2) and in-between (lead 3). The coronary vessel's perfusion
resistance (CVPR) was calculated in arbitrary units as follows:
PP/flow/heart weight. Following the protocol above, hearts were
subjected to perfusion with the dye Trypan blue (0.1%), in order to
evaluate cellular damage and infarction.
e) Results and discussion
ECG results in vivo demonstrated distinct ECG changes after
pilocarpine injections in an acute stage of PSCP: statistically
significant depressions of R- peak were noted under leads 1 and 2
(47% & 16% of control one respectively). DP16 treatment of PSCP
normalized electrical activity at the acute stage in 5 out of 7
treated rats. It is known that the amplitude of ECG events are
partly connected with the intensity of correspondent physiological
processes. Thus, the pilocarpine-induced change of R-wave and its
normalization by DP16 may reflect the ability of DP16 to cure
ventricular weakness, at least under PSCP. Control rats display
relative normalization of R-wave in 3-14 days after pilocarpine.
However, R normalization apparently was correlated with drastically
increased S-wave depth under lead 3 (36%) and lead 2 (61%). The
last was not statistically significant in view of large
variability. Increase of S-wave depth reflected damage typical of
myocardial ischemia and possibly suggests infarction in Pilocarpine
treated control animals. As during the acute stage of PSCP in the
phase of stabilization, DP16 prevents the appearance of ECG
alterations noted in control rats. The difference between animals
protected with DP16 and those not protected, is statistically
significant (p<0.01). In this period of PSCP there is marked
elevation of Heart Rate in both control Pilocarpine, and in DP16
treated animals. Such tachycardia possibly is connected with
hemodynamic insufficiency, which is characteristic for infarction
pathophysiology . Thus, in vivo ECG investigation during long-term
period after Pilocarpine injections revealed definite alteration of
cardiac functions (PSCP), which in some animals may be cured by
DP16-treatment.
f) Langendorff's Heart Model.
In the first 30 min of control, isolated Langendorff's hearts CVPR
steadily increased and this elevation is statistically significant
after 20 min. In all hearts, perfused after pilocarpine
administration, initial perfusion flow was larger then in control,
and subsequent CVPR significantly decreased. This decrease of
coronary vessel tone was possibly connected with intracardial
noradrenaline deficiency or paralysis, evoked by hypoxia. Treatment
of rats with DP16 prior to pilocarpine application prevents damage
of CVPR regulation in both the initial and final periods of
perfusion, thus providing evidence relating to the ability of DP16
to normalize coronary vessels function under hypoxic conditions.
Cessation of perfusion for 30 min and subsequent reperfusion is
characterized by the well-known broad class of cardiac damage
events, which we classified with an arbitrary scale. Control hearts
from non-treated control rats generally were restored after
cessation of perfusion with distinct range of alterations (e.g.,
impaired myocardial excitability, conductivity and contractility).
Mean point of recovery in control group is 6.3.+-.0.6 (n=7). Hearts
from pilocarpine-treated rats on different stages of PSCP
demonstrated an increase of the spectrum and severity of
pathological events, as the mean point of recovery was just
3.3.+-.0.8, n=7, p<0.05. Recovery was frequently accompanied by
ventricular fibrillation. Some of the hearts were not restored
completely or restored atrial activity only. DP16 treatment prior
to pilocarpine administrations increased ability of damaged hearts
to restore after reperfusion cessation: the mean point was
6.4.+-.0.6 (n=9). In this group of rats there was an increased
incidence of cases of complete recovery. Thus, DP16 treatment of
pilocarpine-induced heart damage (PSCP) produced a definite
improvement in cardiac function.
4.5) General conclusions.
The prodrug denoted DP16 exhibited significant therapeutic and
protective effects in experimental models of stroke and ischemia as
well as in models of epilepsy, comparable with using the
corresponding drug in conventional form in an amount which is
10.sup.5 -10.sup.6 times the amount when used in the form of the
prodrug of the invention.
Example 5
Preparation of Prodrug-3.
"Prodrug-3" is the name used herein to denote a 1:1 ester of
1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)
with 1-myristylmyristyl alcohol and is prepared as follows. A
solution of BAPTA (0.5 g, 1.05 mmol) in dimethylformamide (25 ml,
freshly distilled over CaH.sub.2), 1-myristylmyristyl alcohol
(0.451 g, 1.1 mmol), N,N'-dicyclohexylcarbodiimide (0.216 g, 1.1
mmol) and 4-dimethylaminopyridine (0.025 g, 0.202 mmol) were
stirred together for two days at room temperature under argon, in a
50 ml flask equipped with a magnetic stirrer. After two hours,
N,N'-dicyclohexylurea began to precipitate. The reaction was
monitored by TLC (90:10 v/v chloroform:methanol); R.sub.f of the
product=0.62. The precipitate was removed by filtration and the
filtrate was concentrated at 35.degree. C. in vacuum. The residue
was extracted with 25 ml of a 2:1:2 v/v mixture of
chloroform:isopropanol:water. The organic layer was separated,
washed with 1% aq. NaCl solution and dried over Na.sub.2 SO.sub.4 ;
it was then evaporated and the residue was passed through a
160.times.30 mm column of Kieselgel 60 (230-400 mesh ASTM), the
desired product being eluted with a 90:10 v/v chloroform:methanol
mixture. The 1-myristylmyristyl alcohol was prepared according to
the method of Molotkovski, V. G. and Bergelson., L. D.
(Biologicheska Chimia, 1982, 8(9): 1256-1262). The
BAPTA-1-myristylmyristyl alcohol ester link in Prodrug-3 is
susceptible to digestion by esterases.
Example 6
Preparation and biological properties of TVA16.
"TVA16" is the name used herein to denote a 1:1 ester of valproic
acid with the phosphorylcholine derivative
ROCH.sub.2 --CH(OH)--CH.sub.2 O--(PO.sub.2)--OCH.sub.2
N(CH.sub.3).sub.2, where R is hexadecanoyl, and was prepared as
follows. A solution of
1-hexadecanoyl-sn-glycero-3-phosphorylcholine (1.04 mmol) in
chloroform (25 ml, freshly distilled over P.sub.2 O.sub.5),
valproic acid (0.159 g, 1.1 mmol), N,N'-dicyclohexylcarbodiimide
(0.216 g, 1.1 mmol) and 4-dimethylaminopyridine (0.025 g, 0.202
mmol) were stirred together for two days at room temperature under
argon, in a 50 ml flask equipped with a magnetic stirrer and glass
beads (10 g, 5 mm diameter). After two hours, N,N'-dicyclohexylurea
began to precipitate. The reaction was monitored by TLC (65:25:4
v/v chloroform:methanol:water); R.sub.f of the product=0.41. The
precipitate and glass beads were removed by filtration and the
filtrate was concentrated at 35.degree. C. in vacuum. The residue
was extracted with 25 ml of a 2:1:2 v/v mixture of
chloroform:isopropanol:water. The organic layer was separated,
washed with 1% aq. NaCl solution and dried over Na.sub.2 SO.sub.4 ;
it was then evaporated and the residue was passed through a
160.times.30 mm column of Kieselgel 60 (230-400 mesh ASTM), the
desired product being eluted with a 65:25:4 v/v
chloroform:methanol:water mixture; R.sub.f =0.4.
A test sample of TVA16 was administered i.p. (0.01 to 100 mg/kg) to
a group of three mice, one hour before an s.c. dose of metrazol (80
mg/kg). An effective dose was the amount which prevented
convulsions (scored 2 points per animal) and/or death (scored 1
point per animal) in the subsequent 30 minutes. On this basis, the
ED.sub.100 could be calculated and is compared to known
anticonvulsants in the following table.
TABLE 1 ______________________________________ Anticonvulsant
activity of known drugs and TVA16 ED.sub.100 ED.sub.100 Compound
(mg/kg) Compound (mg/kg) ______________________________________
chlordiazepoxide 25 muscimol (i.p.) 2.5 diazepam 2.5 nifedipine
>100 diphenylhydanoin >100 nimodipine >300 flunarizine
>300 phenobarbital 50 glutethimide 150 sodium valproate 500
meprobamate 200 verapamil >100 MK-801 0.5 TVA16 20
______________________________________
From the above data it may be seen that TVA16 has significant
anticonvulsant activity and appears to be more than 500.times.as
potent as sodium valproate.
FIG. 8 presents the dose response curves of valproic acid itself,
in comparison to TVA, which clearly shows the improvement obtained
with the prodrug according to the invention. The doses of each of
the two drugs are calculated on the basis of mg of valproic acid
administered per kg body weight of the animal.
Conclusion
The present invention is not to be limited in scope by the specific
embodiments described herein. Indeed, various modifications of the
invention in addition to those described herein will become
apparent to those skilled in the art from the foregoing description
and accompanying figures. Such modifications are intended to fall
within the scope of the claims. Various publications are cited
herein, the disclosures of which are incorporated by reference in
their entireties.
* * * * *